System control unit, led driver including the system control unit, and method of controlling static current of the led driver

Abstract

Embodiments of the present invention provide a light-emitting diode (LED) driver and method of controlling the static current of the LED driver. In some embodiments, the LED driver is configured to calculate output currents of a pulse form using a small number of parameters and adjust a gate control signal using the mean value of the output currents of a pulse form. Accordingly, the LED driver can be used to control a static current that flows through an LED array connected to a circuit on the secondary side of a transformer using a DC voltage or an AC voltage supplied to the primary side of the transformer. In some embodiments, the LED driver includes a power conversion unit, switching unit, transformer, zero current detection unit, and system control unit. In some embodiments, the system control unit is configured to adjust the gate control signal.

What is claimed is: 
     
         1 . A system control unit included in a light-emitting diode (LED) driver, the LED driver also comprising a switching unit, a transformer, and a zero current detection unit, wherein the switching unit comprises a power transistor configured to operate in response to a gate control signal, and a switching resistor placed between the power transistor and a ground voltage, wherein the transformer is configured to transfer an input voltage to a secondary coil of the transformer at a specific ratio in response to a switching operation of the switching unit connected to a primary coil of the transformer, and wherein the zero current detection unit is placed on a primary side of the transformer and is configured to generate a resonant voltage into which voltage that drops to an LED array connected to the secondary coil and voltage that drops to a diode connected to the secondary coil are incorporated,
 wherein the system control unit is configured to:
 estimate a second peak value that is a highest value of currents flowing through the diode using current flowing through the power transistor; 
 calculate a mean value of currents supplied to the LED array for a specific time interval using a point of time at which the power transistor is turned off, a point of time at which the diode is turned off, and the second peak value; and 
 update the gate control signal using the mean value, 
   wherein the system control unit is configured to determine the point of time at which the power transistor is turned off by using the gate control signal.   
     
     
         2 . The system control unit of  claim 1 , wherein the system control unit comprises:
 a diode current peak value estimator configured to detect a first peak value that is a highest value of the currents flowing through the power transistor and estimate the second peak value using the first peak value;   a diode turn-off time point detector configured to detect the point of time at which the diode is turned off using the resonant voltage;   a power transistor turn-off time point detector configured to detect the point of time at which the power transistor is turned off using the gate control signal;   a mean value calculator configured to generate the mean value of output currents of a pulse form corresponding to the currents supplied to the LED array for the specific time interval, using the point of time at which the power transistor is turned off, the point of time at which the diode is turned off, and the second peak value; and   a pulse width modulation (PWM) controller configured to update the gate control signal using the mean value.   
     
     
         3 . The system control unit of  claim 2 , wherein:
 the diode current peak value estimator is configured to estimate the second peak value using a product of a ratio of a number of turns of the primary coil and a number of turns of the secondary coil that form the transformer and the first peak value; and   the specific ratio is the ratio of the number of turns of the primary coil and the number of turns of the secondary coil that form the transformer.   
     
     
         4 . The system control unit of  claim 2 , wherein:
 the output currents of a pulse form have a pulse width ranging from the point of time at which the power transistor is turned off to the point of time at which the diode is turned off; and   a size of the pulse is half the second peak value.   
     
     
         5 . The system control unit of  claim 2 , wherein the mean value calculator comprises a low pass filter configured to receive the output currents of a pulse form for the specific time interval and to generate the mean value using the output currents. 
     
     
         6 . The system control unit of  claim 1 , wherein the current flowing through the power transistor is estimated using voltage that drops between the power transistor and the switching resistor and a resistance value of the switching resistor. 
     
     
         7 . An LED driver, comprising:
 a power conversion unit configured to generate an input voltage by rectifying a supply voltage of an AC form;   a switching unit comprising a power transistor configured to operate in response to a gate control signal, and a switching resistor placed between the power transistor and a ground voltage;   a transformer configured to transfer the input voltage or a supply voltage of a DC form to a secondary coil of the transformer at a specific ratio in response to a switching operation of the switching unit connected to a primary coil of the transformer;   a zero current detection unit placed on a primary side of the transformer and configured to generate a resonant voltage into which voltage that drops to an LED array connected to the secondary coil and voltage that drops to a diode connected to the secondary coil are incorporated; and   a system control unit configured to:
 estimate a second peak value that is a highest value of currents flowing through the diode using current flowing through the power transistor; 
 calculate a mean value of currents supplied to the LED array for a specific time interval using a point of time at which the power transistor is turned off, a point of time at which the diode is turned off, and the second peak value; and 
 update the gate control signal using the mean value, 
   wherein the system control unit is configured to determine the point of time at which the power transistor is turned off by using the gate control signal.   
     
     
         8 . The LED driver of  claim 7 , wherein the system control unit comprises:
 a diode current peak value estimator configured to detect a first peak value that is a highest value of the currents flowing through the power transistor and estimate the second peak value using the first peak value;   a diode turn-off time point detector configured to detect the point of time at which the diode is turned off using the resonant voltage;   a power transistor turn-off time point detector configured to detect the point of time at which the power transistor is turned off using the gate control signal;   a mean value calculator configured to generate the mean value of output currents of a pulse form corresponding to the currents supplied to the LED array for the specific time interval, using the point of time at which the power transistor is turned off, the point of time at which the diode is turned off, and the second peak value; and   a PWM controller configured to update the gate control signal using the mean value.   
     
     
         9 . The LED driver of  claim 8 , wherein:
 the diode current peak value estimator is configured to estimate the second peak value using a product of a ratio of a number of turns of the primary coil and a number of turns of the secondary coil that form the transformer and the first peak value; and   the specific ratio is the ratio of the number of turns of the primary coil and the number of turns of the secondary coil that form the transformer.   
     
     
         10 . The LED driver of  claim 8 , wherein:
 the output currents of a pulse form have a pulse width ranging from the point of time at which the power transistor is turned off to the point of time at which the diode is turned off; and   a size of the pulse is half the second peak value.   
     
     
         11 . The LED driver of  claim 8 , wherein the mean value calculator comprises a low pass filter configured to receive the output currents of a pulse form for the specific time interval and to generate the mean value using the output currents. 
     
     
         12 . The LED driver of  claim 7 , wherein the specific time interval is determined by a frequency of the AC voltage. 
     
     
         13 . The LED driver of  claim 7 , wherein the current flowing through the power transistor is estimated using voltage that drops between the power transistor and the switching resistor and a resistance value of the switching resistor. 
     
     
         14 . A method of controlling a static current of an LED driver according to  claim 7 , the method comprising:
 a parameter extraction step of detecting a first peak value that is a highest value of the currents flowing through the power transistor, detecting the second peak value that is a highest value of the currents flowing through the diode, detecting the point of time at which the power transistor is turned off, and detecting the point of time at which the current flowing through the diode becomes 0;   a pulse form output current generation step of generating output currents of a pulse form using the second peak value, the point of time at which the power transistor is turned off, and the point of time at which the current flowing through the diode becomes  0 ;   a mean value generation step of generating the mean value of output currents included in the specific time interval; and   a gate control signal adjustment step of adjusting the gate control signal using the mean value.   
     
     
         15 . The method of  claim 14 , wherein the second peak value that is the highest value of the currents flowing through the diode is determined by a product of a ratio of a number of turns of the primary coil and a number of turns of the secondary coil that form the transformer and the first peak value. 
     
     
         16 . The method of  claim 15 , wherein:
 the output currents of a pulse form have a pulse width ranging from the point of time at which the power transistor is turned off to the point of time at which the diode is turned off; and   a size of the pulse is half the second peak value.   
     
     
         17 . The method of  claim 15 , wherein the specific time interval is determined by a frequency of an AC voltage. 
     
     
         18 . The method of  claim 14 , further comprising a specific time interval determination step of performing the parameter extraction step and the pulse form output current generation step if the output current of a pulse form is included in the specific time interval, and performing the mean value generation step if the output current of a pulse form is not included in the specific time interval. 
     
     
         19 . The method of  claim 18 , wherein the parameter extraction step, the pulse form output current generation step, the specific time interval determination step, the mean value generation step, and the gate control signal adjustment step are repeatedly performed while the LED driver supplies a static current to the LED array. 
     
     
         20 . The method of  claim 14 , wherein the current flowing through the power transistor is estimated using voltage that drops between the power transistor and the switching resistor and a resistance value of the switching resistor.